An air pollution control apparatus processes flue gas in various plants and boilers, and generally includes an absorber that serves as a passage for the flue gas; an absorbent spraying unit that sprays an absorbent into the absorber; and a reservoir tank that reserves therein the absorbent. The flue gas is processed by being brought into gas-liquid contact with the absorbent, while sending the flue gas from the lower area to the upper area of the absorber (or from the upper area to the lower area). After processing the flue gas, the absorbent is collected and reserved in the reservoir tank.
If a plant uses heavy oil as a fuel, for example, unburned fuel contained in the flue gas becomes concentrated in the reservoir tank, and produces foams in the absorbent. The amount of produced foams cannot be controlled by an apparatus design or an operation condition, because such an amount depends on factors such as the fuel and the absorbent. If a large amount of foams is produced, a flue gas processing pressure loss could rise abnormally, or the foams might overflow, to damage equipments. Therefore, a conventional air pollution control apparatus extracts and breaks the foams produced in the absorbent. Known examples of the conventional air pollution control apparatus having such a structure are disclosed in Japanese Patent No. 3388984 and Japanese Patent No. 3392660.
In a recent air pollution control apparatus, an entrance is provided on the side of the absorber for guiding the flue gas into the absorber, and a flue gas duct is connected to the entrance. In such a structure, the flue gas enters the absorber from the entrance, and flows through the absorber, from the lower area to the upper area. Such a structure improves a desulfurization efficiency of the flue gas, in comparison with a structure in which the flue gas is guided into the absorber from the upper area. Known examples of a conventional air pollution control apparatus having such a structure are disclosed in Japanese Patent Application Laid-open No. 2005-193133 and Japanese Patent Application Laid-open No. 2005-211792.